Here is a great article on how to build your own Cupola. These free cupola plans are from The Family Handyman magazine. If you have ever admired the look of a structure with a Cupola, you will appreciate this free plan. This is a very visual plan. Each step is accompanied by pictures to make this a relatively easy project to build.
The free cupola plans include a measured drawing that is in the classic Family Handyman format that includes a part exploded view with very clear measurements.
This cupola would look terrific on your garage or outbuilding.